The present invention relates to control valves that are used to control displacement in, for example, variable displacement compressors. More particularly, the present invention relates to a control valve that has a valve body and a solenoid for moving the valve body and is capable of maintaining satisfactory conductivity of the solenoid.
A variable displacement compressor typically has a displacement control valve that is arranged in a supply passage that connects a discharge chamber and a crank chamber. The control valve alters the opening amount of the supply passage to control the amount of refrigerant gas sent from the discharge chamber to the crank chamber thereby adjusting the pressure in the crank chamber. This alters the difference between oppositely directed pressures acting on a set of pistons, that is, the difference between the crank chamber pressure and the pressure in the cylinder bores. The pressure difference changes the inclination of a swash plate and thus varies the compressor displacement.
The control valve has a valve body for adjusting the opening amount of the supply passage and a solenoid for moving the valve body. A controller excites and de-excites the solenoid by means of a drive circuit based on various operating conditions such as the cooling load applied to the compressor. The valve body is moved to alter the opening amount of the supply passage based on the excitation and de-excitation of the solenoid. This adjusts the amount of refrigerant gas sent from the discharge chamber to the crank chamber.
As shown in FIGS. 15 and 16, the solenoid of a control valve has a coil unit 112. The coil unit 112 includes a cylindrical bobbin 113 made of an insulating synthetic resin and a coil 114 wound about the bobbin 113. A base plate 115 extends laterally from the lower portion of the bobbin 113. A power supply plate 116 and a ground plate 117 are fixed to the lower surface of the base plate 115. The coil 114 has an end that defines a terminal wire 114a leading to the power supply plate 116 and another end that defines a terminal wire 114b leading to the ground plate 117. The power supply plate 116 includes a clamping block 116a to clamp the terminal wire 114a. The ground plate 117 includes a clamping block 117a to clamp the terminal wire 114b. The ground plate 117 is connected to a grounded member.
The clamping blocks 116a, 117a are located at the distal end of the base plate 115. This facilitates the attachment of the terminal wires 114a, 114b to the associated clamping blocks 116a, 117a. The terminal wires 114a, 114b extend from the bobbin 113 toward the underside of the base plate 115 and past the plates 116, 117 to be connected to the associated clamping blocks 116a, 117a.
The power supply plate 116 includes a cathode holder 116b and a pin holder 116c. The ground plate 117b includes an anode holder 117b. A connector pin 118 is fixed to the pin holder 116c by a solder 121. A power supply wire (not shown) provided with a connector at its distal end extends from a drive circuit for driving the solenoid. The connector is engaged with the connector pin 118 such that the connector pin 118 is detachably connected to the drive circuit by means of the power supply wire.
A diode 119 is fixed to the cathode holder 116b and the anode holder 117b. The diode 119 has a cathode terminal 119a fixed to the cathode holder 116b by solder 122 and an anode terminal 119b fixed to the anode holder 117b by solder 122. The diode 119 functions to protect the drive circuit. When electric current from the drive circuit stops, self-inductance produces counterelectromotive force in the coil 114. The current resulting from the counterelectromotive force is consumed by a closed circuit formed between the coil 114 and the diode 119 and does not enter the drive circuit. This prevents excessive electric load produced by counterelectromotive force from being applied to the drive circuit.
As shown in FIG. 15, the coil unit 112 is surrounded by insulating coating 120 made of synthetic resin. The coil 114, the base plate 115, the plates 116, 117, the diode 119 are immersed in the coating 120. This improves the insulation characteristics and weather resistance of the coil unit 112.
The base plate 115 is integrally formed with the bobbin 113. The bobbin 113, the base plate 115 and the coating 120 are made of synthetic resins, which have a greater coefficient of thermal expansion than that of metal. Heat generated by excitation of the solenoid causes the resin members to expand. The thermal expansion enlarges the space between the clamping blocks 116a, 117a of the plates 116, 117 and the coil 114 wound about the bobbin 113. The coil 114 is made of conductive metal and is not expanded by heat as much as the resin members. The thermal expansion of the resin members therefore results in tension acting on the coil's terminal wires 114a, 114b held by the clamping blocks 116a, 17a. This may bread the terminal wires 114a, 114b, which have relatively weaker tensile strength.
As shown in FIGS. 17A and 17B, the terminal wire 114b directly contacts an edge 117c of the ground plate 117, and the terminal wire 114a directly contacts an edge 116d of the power supply plate 117. Thus, when receiving tension, or when stretched, the terminal wires 114a, 114b are pressed against the edges 116d, 117c. Also, assembly of the coil unit 112 may cause he terminal wires 114a, 114b to be pressed against the edges 116d, 117c. As a result, the terminal wires 114a, 114b may be damaged or broken.
Temperature changes expand or contract the base plate and the coating 120. Expansion and contraction of the plate 115 and the coating 120 change the distance between the cathode holder 116b of the power supply plate 116 and the anode holder 117b of the ground plate 117. However, like the coil 114, the terminals 119a, 119b of the diode 119 are made of conductive metal. Therefore, the length of the diode 119 is changed little by temperature changes. Changes of the distance between the cathode holder 116b and the anode holder 117b apply a reactive force to the solder 122, which fixes the terminals 119a, 119b to the holders 116b, 117b. The reactive force wears the solder 122 and degrades the bonding strength between the terminals 119a, 119b and the holders 116b, 117b. This mad result in unsatisfactory electrical conductivity between the terminals 119a, 119b and the holders 116b, 117b.
During installation of the compressor in a vehicle or during a maintenance of the compressor, the connector, which is attached to the distal end of the power supply wire extending from the drive circuit, is connected to and is disconnected from the connector pin 118 of the solenoid. Such connection and disconnection applies reactive force to the solder 121, which fixes the connector pin 118 to the pin holder 116c. The reactive force wears the solder 121 and degrades the bonding strength between the connector pin 118 and the pin holder 116c. This may result in unsatisfactory electrical conductivity between the connector pin 118 and the holder 116c.